My thoughts are that experience is a great asset, but it doesn't necessarily have to be work experience. While I think the value of work experience to strengthen an application is large, it still falls under the embrella of showing an ad committee that you have a genuine interest in the field. Volunteer experiences, research experiences, extra-curricular experiences... can all be public health related and and help articulate exactly why you would succeed in a specific program; experiences of any sort play a large role in having defined one's skill set, one's career goals, one's emotional and intellectual curiosity towards a certain field. I myself had limited work experience in public health, but showed via other experiences why I'd be a great fit for the program I've been accepted to.